The present invention relates to a method of manufacturing a speaker edge member.
The present application claims priority from Japanese Application No. 2005-373232, the disclosure of which is incorporated herein by reference.
A speaker for reproducing music or the like has a general structure shown in FIGS. 1A, 1B, and FIG. 2 (disclosed in Japanese Unexamined Patent Application Publication No. 2003-111189). As shown, the conventional speaker has a magnetic circuit 1 formed by including a magnet 2, a lower plate 3, and an upper plate 4. An annular magnetic gap is formed between the upper plate 4 and a center pole 5 uprightly standing in the center of the lower plate 3. A coil bobbin 6 wound by a voice coil 7 is provided in a manner such that the voice coil 7 is located with in the magnetic gap. Further, the coil bobbin 6 is connected with one edge of a damper 11, while a damper support portion 11a supporting the other edge of the damper 11 is connected with a speaker frame 10, so that the voice coil 7 can be properly held within the magnetic gap of the magnetic circuit 1. Moreover, a center cap 8 is provided on an upper end of the coil bobbin 6, while a central portion of a diaphragm 20 is fixed near the upper end of the coil bobbin 6. In addition, an annular edge member 21 is connected to an outer edge portion of the diaphragm 20, so that the diaphragm 20 can be attached, by virtue of the annular edge member 21, to an upper portion of the speaker frame 10 mounted on the upper plate 4.
The annular edge member 21 is formed with an annular outer edge portion 21A which is used to attach the annular edge member 21 to an attachment surface 10b formed on an inner side of an edge portion 10a of the speaker frame 10. Such an outer edge portion 21A is integrally formed with the annular edge member 21 by virtue of pressurized molding using urethane or a rubber, has a desired thickness and faces inwardly. The bottom surface of the outer edge portion 21A is attached to the attachment surface 10b of the speaker frame 10, while its outer periphery surface 21a is attached to the inner side of the edge portion 10a of the speaker frame 10. FIG. 2 is a sectional view taken along B-B line shown in FIG. 1A. As shown in FIG. 2, an attachment screw 14 for attaching the speaker frame 10 to an attached member is provided on an inner attachment surface 10b inwardly of the edge portion 10a of the speaker frame 10. Here, the outer edge portion 21A has a thickness which is larger than that of the head of the attachment screw 14. Further, as shown in FIG. 1A and FIG. 2, a notch 21b is formed to avoid an undesired contact between the outer edge 21A and the attachment screw 14.
In fact, the annular edge member 21 is provided to resiliently support the outer edge portion of the speaker diaphragm 20 on the speaker frame 10. On the other hand, such an annular edge member 21 is required to have a holding function for holding the diaphragm 20 in a predetermined position, a linear displacement function (linearity) for linearly displacing the outer edge portion of the diaphragm with respect to a driving force acting on the diaphragm 20, a braking function for preventing a lateral vibration of the diaphragm 20, and an air tight function (air tightness) for preventing a back surface reflection sound wave from emitting to the front surface of the diaphragm. Further, since a vibration of the diaphragm will cause a vibration in the annular edge member 21 itself, it is important for the annular edge member 21 not to cause an inherent resonance. For this reason, a material and a shape of the annular edge member 21 are usually set in accordance with a performance required by each speaker, by taking into account the foregoing functions.
However, with regard to a high power high-output speaker such as sub-woofer, its diaphragm usually has a large vibration and thus there is a large negative pressure within a speaker cavity. As a result, an edge member, which should be kept in a convexly rolled shape, will become inwardly concave, undesirably causing a so-called “inward suction.” When there is such an “inward suction,” an edge shape designed for effecting a linear diaphragm displacement and preventing a lateral vibration and an inherent vibration of diaphragm, will get collapsed. At this time, the diaphragm 20 will cause an abnormal vibration and edge member itself will have an inherent resonance, resulting in a problem that a distorted or abnormal sound would occur in a low-pitched sound area.
On the other hand, Japanese Unexamined Patent Application Publication No. 2004-7357 has disclosed an edge member containing a substrate consisting of cloth, fiber or the like, with it rigidity improved to alleviate the above-mentioned problems. Specifically, this published patent application has disclosed a method in which an edge member 21 shown in FIG. 1 can be fabricated simply by virtue of insertion molding, which will be discussed as follows with reference to the accompanying drawings.
As shown in FIG. 3A, an edge member molding die 203 comprises a male die 203A, a female die 203B, as well as a core die 203C. At first, the male die 203A and the female die 203B are separated from each other. Then, edge member formation material 21A′ serving as raw material for forming an edge member 21 is introduced into the female die 203B, a substrate 201B is placed over the edge member formation material 21A′, and the core die 203C is interposed between the male die 203A and the female die 203B. Here, the substrate 201B is a member formed by impregnating a natural fiber with a thermosetting resin, followed by cutting the impregnated material into annular members.
Subsequently, as shown in FIG. 3B, the male die 203A and the female die 203B are closed towards each other and a heating/pressurizing treatment is carried out, thereby obtaining a speaker edge member 21′ containing the substrate 201B.
However, when the above-mentioned insertion molding is performed, the substrate 210B will undesirably protrude beyond a parting line 204, as shown in FIGS. 3B and 3C, resulting in a low strength at the protruding portion and thus causing the edge member to be broken or suffer from some other troubles. Besides, after the foregoing insertion molding, it is necessary to carry out an additional step in which a cutter has to be used to cut off an unwanted substrate portion protruding beyond the parting line 204, thus requiring an additional time and an additional cost for carrying out such an additional step.